How I can use generated headers (like from messages) from one package in another?

edit

I'm using groovy + catkin. How can I include the devel/include<package_name>, which contains e.g. the generated header-files from the messages in another package?

find_package(package_name REQUIRED)

and

include_directories(include
  ${catkin_INCLUDE_DIRS}
  ${Boost_INCLUDE_DIRS}
  ${merlin_messages_INCLUDE_DIRS}
)

doesn't seem to be enough, I suppose that this include only the headers which come from this package, but not the automatically generated one?